Aqueous extracts of commercially prepared acetone powders or fresh lung tissue will be subjected to large scale ultrafiltration, using a newly developed Millipore ultrafilter system capable of handling large volumes of material. These fractions will be collected primarily between 1,000 and 100,000 daltons in this system. This fraction will, in turn, be subdivided by further ultrafiltration, using 50,000 dalton filters, and nondialyzable material which passes through this filter contains fibroblast chalone activity. After ribonuclease treatment, the chalone activity will be further purified by ammonium sulfate fractionation, isoelectric focusing, and preparative acrylamide gel electrophoresis. The activity of these fractions will be determined using established cell line of human osteosarcoma cells in vitro. The amount of lyophilized material required to inhibit 50% of the H3-thymidine uptake into acid insoluble DNA will constitute the quantitative endpoint. The purity of the resulting material will be assessed, using polyacrylamide gel electrophoresis at three different pH and SDS gel electrophoresis as well. The molecular weights will be calculated both from electrophoretic mobility and exclusion chromatography. The carbohydrate and amino acid composition of this purified chalone will be determined.